Developments in renewable energy, mining and quarrying, oil exploration, marine and other applications have led to significant increases in the size of power transmission components — like gears, shafts, pinions and bearings, to handle greater productivity demands. As these large components are exposed to severe duty cycles, there is renewed emphasis on the heat-treating methods needed to enhance their wear resistance and strength properties. 

Estimated by industry sources to represent around 10% of component manufacturing costs, heat treatment modifies the microstructure of metallic materials, influencing mechanical characteristics like strength, ductility, toughness, hardness, and wear resistance. Thus, it increases the service life and technical performance of metal parts, which is even more critical for this new generation of larger components that are crucial to mechanical function and usually difficult to replace. 

Anticipating growing customer demand for processing larger gears, shafts and other components, a commercial heat-treater that specializes in such products — Keighley Laboratories in West Yorkshire, England — recently expanded the holding capacity of one of its largest pit furnaces. By increasing the chamber’s dimensions to 1,110-mm working diameter and almost 1,800-mm maximum length, it gained over 30% in overall heat treating capacity. At the same time it carried out a capacity upgrade for the overhead crane that serves all seven pit furnaces on the site, as well as a salt bath and tempering equipment. The crane now has a maximum lift of 3.0-metric tons. 

Enlarging the No. 1 pit furnace involved custom-fabricating an inner shell (or retort) made from duplex stainless steel, but this considerable investment has already been offset by some significant new orders: Keighley was contracted to heat treat 1,108-mm diameter gear wheels for an offshore project; and a 1,755-mm long, 1-mt shafts for a renewable energy project.

The company already has started to study upgrading other pit furnaces there, and its programmable process controllers, too. 

“This has opened up a new market for us amongst engineering companies and OEMs, who are looking to heat treat larger components,” offered Michael Emmott, the commercial director. “This involves physical issues regarding accommodating the size of these parts, then lifting them out of the furnace and into the quench tank, as well as demanding special skills for treating very large workpieces without damage or distortion.”

Keighley Labs’ furnaces perform various heat-treating processes, including carburizing, carbonitriding, hardening and tempering, stress relieving, homogenizing and carbon restoration, working at temperatures up to 980°C. The operation handles steel, iron, high chrome iron, cast iron, ADI, and alloy steel materials. The products are used in numerous manufacturing sectors, including aerospace, marine, defense, rail, quarry and construction, energy, and general engineering companies. 

Pit furnaces are vertically oriented batch furnaces, with the thermal-process section buried in a pit and extending up to floor level. A hydraulically operated, sealed cover extends above the surface. Workpieces are held in a jig or charge basket in the furnace, the inner retort protecting them from the direct radiation of heat. This configuration is particularly well suited to treating long parts, such as shafts, tubes and rods, although a wide variety of shapes and sizes can be accommodated, individually or in batches.